Our macaw is a rescue, and came to us knowing to go back to a perch and not poop on a person. Yours may think that sending poop far outside the cage is cleaner than dropping it inside. If I had to poop in a cage, there's no monkey could beat me for flinging distance.
Large parrots really do require a tremendous amount of energy and attention to be good companions. There is a lot of training that must be done, which requires both the human and the parrot to understand one another. This takes time: a lot of focused time on the part of the human, who lives outside that cage and has all the real power in the relationship, to learn to understand what the bird needs and wants and figure out how to move things in the right direction. There is no quick fix or easy solution. It's either spend multiple hours a day learning to partner with the bird, or go on the way things are.
It doesn't sound as if things are going that great. It may be that you just don't have the time and energy for the parrot. To relinquish care for a young parrot like this is not good, but it is better than a world where the parrot doesn't have loving interactions and a stimulating, engaged life with its human. You sort of have to come to crisis with this, and decide if you are willing and able to do a complete 180 turn around in your relationship, and commit to the bird. If you do that, you may have a long road ahead of you and many difficult hours but in the end you will have a relationship like no other. If not, then it would be best for your parrot to post in the other forum and ask for a new caregiver to accept your bird. Your bird will be happier and you will be happier.
Only remember: never get another parrot. Think what you would say to a parent who sent their child to the orphanage because it wasn't potty trained by age seven, then decided to have another child. A new parrot won't be any easier or less demanding. If they do start off easier, they will likely go to the same place - because the relationship depends 90% on you and only 10% on the bird. It's not fair to an innocent parrot to put them into a situation where they are likely to wind up being abandoned. A parrot is a lifetime comittment: to love and honor and cherish just as in a marriage. You might find the smaller birds, who have less need of interaction and smaller poops, to be a better fit, but birds are not ornaments to our lives. They are living creatures with hearts and minds and needs.
I myself am not a good parrot person. I don't want to give up as much of my free time and attention for seventy years with a flying toddler with a knife on its face. I do the best I can with the bird I am partly responsible for, and lean heavily on the members of this forum for understanding and support when I am feeling like a failure. They keep me lifted up, which helps me to do right by the bird. If you wish to make a deep revolution in your relationship with your own bird I am sure you will find the same loving support as I find. Alternatively I know you will be supported in finding a good placement for your macaw. There's no shame in letting him go to a better situation for you both.